Flotation Behavior and Mechanism of Andalusite and Quartz Under the Sodium Dodecyl Sulfonate System

Abstract

The paper systematically investigated the flotation behavior and interaction mechanisms of andalusite and quartz under sodium dodecyl sulfonate (SDS) through integrated experimental and computational approaches, including zeta potential measurements, Fourier-transform infrared (FTIR) spectroscopy, Materials Studio (MS)-based quantum chemical calculations, and single-mineral flotation tests. The results of zeta potential and infrared spectroscopy analysis indicated that SDS underwent strong chemical adsorption on the surface of andalusite, while the adsorption effect on the surface of quartz was not obvious. MS calculations showed that the {100} surface energy of andalusite was the lowest, and it was the most important dissociation surface. After SDS was adsorbed on the {100} surface of andalusite, the aluminum atoms on the surface of andalusite lost electrons, resulting in a significant increase in the number of positive charges they carried. The activity of oxygen atoms was enhanced, while the number of charges carried by silicon atoms changed relatively little. It was indicated that SDS adsorbed the active sites of Al atoms on the surface of andalusite. The results of the pure mineral flotation test further verified the accuracy of the previous test results, indicating that andalusite and quartz had a good flotation separation effect under the SDS system.

1. Introduction

Andalusite is an aluminosilicate mineral with the chemical formula Al₂O₃·SiO₂. Due to its excellent chemical corrosion resistance and stability, it is widely utilized in industrial fields such as aerospace, shipbuilding, and metallurgy [1,2,3]. The geological exploration and mining development of andalusite deposits in China remain underdeveloped, with a limited number of proven deposits currently identified. Consequently, the domestic supply of andalusite concentrate still heavily relies on large-scale imports from overseas markets. The majority of domestic andalusite ores are characterized by low-grade quality and complex mineral composition [4,5,6,7], while underdeveloped beneficiation technologies further result in insufficient capacity to consistently meet market demands. To obtain qualified-grade andalusite concentrate, it is essential to apply integrated beneficiation processes to efficiently remove deleterious impurities to the maximum extent. Weakly magnetic minerals such as biotite, rutile, and garnet can be separated through wet high-intensity magnetic separation. Both quartz and andalusite are non-magnetic minerals with closely matched specific gravity, rendering magnetic separation and gravity concentration ineffective for their selective separation. Thus, in the beneficiation of andalusite, the flotation process serves as an effective approach for achieving highly efficient separation between andalusite and quartz [8]. Therefore, intensifying research on the flotation separation of andalusite and quartz is of critical importance for advancing the development of China’s andalusite beneficiation industry.

Andalusite, kyanite, and sillimanite belong to the aluminosilicate mineral group with identical chemical formula Al₂SiO₅, representing polymorphic phases within the kyanite mineral series [9,10]. The crystal structure of andalusite belongs to the orthorhombic system with a nesosilicate framework. Typically formed under moderate temperature and pressure conditions, andalusite undergoes an irreversible crystalline phase transformation when heated under ambient pressure. This reaction produces acicular mullite crystals oriented parallel to the original crystal lattice, while maintaining dimensional stability upon cooling. The resulting mullite exhibits exceptional refractoriness exceeding 1800 °C, it exhibits outstanding chemical stability and corrosion resistance [11,12,13], coupled with high mechanical strength, low thermal conductivity, excellent thermal shock resistance, superior slag corrosion resistance under high-temperature conditions, and a high load softening point [14,15,16,17,18]. It also demonstrates remarkable resistance to dissolution in hydrofluoric acid (HF) solutions [19]. These properties make andalusite a critical raw material for manufacturing unfired refractories [6,20] and refractory bricks [20]. However, global andalusite reserves remain scarce, with South Africa, the United States, and China currently serving as the leading producers of this strategic industrial mineral [21,22].

Current beneficiation methods for andalusite include gravity separation and magnetic separation for coarse-grained ores with large single crystals to obtain rough concentrates. However, for most fine-grained andalusite ores characterized by complex mineralogy and similar specific gravity to gangue minerals, flotation processes are generally employed for enrichment. Prior to flotation, thorough desliming and impurity removal are essential to mitigate adverse effects on concentrate recovery. Internationally, flotation remains the predominant industrial practice for andalusite beneficiation [23,24]. Numerous reagents are applied in andalusite flotation pulp systems, categorized into acidic and alkaline regimes based on mineral surface charge characteristics. Under acidic conditions (pH 3–4), amine cationic collectors (e.g., dodecylamine acetate), oleic acid, linoleic acid, naphthenic acid, or alkyl sulfonates are primarily employed to float andalusite, while depressants such as citric acid, lactic acid, and sodium silicate effectively suppress quartz and other gangue minerals. Under neutral conditions (pH = 7), selective leaching of surface aluminum ions with dilute acid pretreatment enables effective andalusite collection using cationic collectors such as dodecylamine acetate. In the alkaline range (pH 8–10), carboxylate collectors (e.g., sodium oleate) become the preferred reagents for andalusite flotation [24,25,26]. Zhou Lingchu et al. [27] conducted comparative studies on direct and reverse flotation processes for an andalusite ore from the Yangnaigou mining area, Xixia County, Henan Province. Their findings revealed that direct flotation using sodium petroleum sulfonate as the collector achieved significantly superior beneficiation performance compared to reverse flotation with dodecylamine. Research findings [28] reveal that quartz, as the primary gangue mineral associated with andalusite, typically constitutes 30–50% of the ore composition. The presence of quartz significantly deteriorates the quality of andalusite concentrates.

This study systematically investigates the flotation behavior of monomineral andalusite and quartz in a SDS system. Through zeta potential measurements, infrared spectroscopy, and quantum chemical calculations, the interaction mechanisms between the collector SDS and andalusite were elucidated, providing a theoretical foundation for guiding the efficient separation of andalusite from quartz.

2. Experimental

2.1. Materials and Reagents

The pure andalusite and quartz samples were taken from an andalusite mine in Gansu. High-purity massive ores were selected and ground to less than 2 mm with a dry agate grinder (Fuxin Weicheng Agate Products, Fuxin, China). The −0.074 + 0.038 mm particle size fraction was screened out, then washed with deionized water and air-dried under natural conditions. Clean ground glass stopper bottles were selected for sealed storage and standby. The results of chemical composition analysis show (

Table 1. Chemical compositions of andalusite and quartz (%).

Mineral	SiO2	Al2O3	TFe	MgO	TiO2	K2O	Ignition Loss
Andalusite	37.68	61.25	0.25	0.083	0.59	0.17	1.03
Quartz	97.69	0.17	0.06	0.50	-	0.26	-

) that the content of Al₂O₃ in the andalusite sample is 61.25% and the content of SiO₂ is 37.68%; the content of SiO₂ in the quartz sample is 97.96%. Combined with the XRD pattern analysis (Figure 1), it can be seen that the diffraction pattern of the andalusite single mineral contains a small amount of impurity peaks of quartz crystals, while the diffraction pattern of the quartz single mineral shows no impurity peaks of other crystal forms, meeting the requirements for sample purity of single mineral specimens.

2.2. Test Methods

2.2.1. Zeta Potential Measurements

The single mineral sample was ground to less than 2 microns, 0.03 g of the ground sample was weighed and placed in a beaker, 40 mL of pre-prepared pH adjustment solution was added to it, the agent was added, and the magnetic stirrer was stirred for 5 min, and then a small amount of suspension was taken and measured on the ZP-7020 Zeta potentiometer (Colloidal Dynamics, Shanghai, China).

2.2.2. Infrared Spectroscopic Analysis

The sample to be tested was ground to less than 2 microns, 2 g of the sample was put into a high-concentration collector solution with adjusted pH value, and stirred thoroughly. The concentration of the collector was 2.5 × 10⁻³ mol/L and dried naturally after dehydration to prepare the sample to be tested. The sample to be tested was mixed with 1:100 potassium bromide powder and pressed into small discs by a tablet press, and the pressed sample was placed on the sample holder for infrared spectroscopy testing.

2.2.3. MS Calculation Method

Based on DFT as the theoretical basis of calculation, the Castep module in Materials Studio 8.0 software was used to establish the ideal unit cell of andalusite, the structure of the self-built andalusite unit cell was optimized, the geometric structure of the surface model of andalusite and the adsorption model of SDS molecule on the surface of andalusite was optimized by using the dmol3 module, the mulliken charge analysis was carried out on the adsorption model after structural optimization, and the electronic density of states of atoms near the adsorption point was analyzed.

2.2.4. Single-Mineral Flotation Tests

The single mineral flotation test was carried out in a 40 mL XFG flotation cell (Jilin Prospecting, Changchun, China), and the flotation machine impeller speed was set to 1760 rpm. An amount of 2.0 g of sample for each test was placed in a 50 mL beaker, and an appropriate amount of deionized water was added and treated in an ultrasonic cleaner for 5 min. After standing for clarification, the supernatant liquid was decanted to complete the desliming step. Subsequently, 40 mL of deionized water was poured into the flotation hanging tank for 1 min, the pH was adjusted with H₂SO₄ or NaOH, and then the collector was added in turn after stirring for two minutes. The slurry time was 3 min for each slurry adjustment time, and the flotation time was 3 min; the products in the tank and the foam products were filtered, dried, and weighed, respectively, to calculate the recovery rate. This is shown in Figure 2.

3. Result and Discussion

3.1. Variations in Surface Zeta Potential of Andalusite and Quartz Under SDS Treatment

Zeta potential measurements of andalusite and quartz were conducted under varying pH conditions in both deionized water and SDS solution. As shown in Figure 3, in deionized water, the surface zeta potentials of both minerals gradually decreased with increasing pH, with their points of zero charge (PZC) observed at approximately pH 5.2 for andalusite and pH 2.1 for quartz. When the pH was below their respective points of zero charge (PZC), the andalusite surface exhibited a positive zeta potential. Conversely, when the pH exceeded the PZC, both andalusite and quartz surfaces displayed negative zeta potentials [23]. Based on the optimal pH of 3 determined from single-mineral flotation tests, the addition of SDS induced a significant negative shift in the zeta potential of andalusite, while that of quartz remained virtually unchanged. This demonstrates that dodecyl sulfonate anions from SDS specifically adsorb onto the andalusite surface, inducing substantial modifications to its interfacial electrical properties, while minimal interaction occurred with the quartz surface.

3.2. Infrared Spectroscopy Analysis Under the Action of SDS

Studies demonstrate that alkyl sulfonic acids with lower molecular weights underwent only physisorption on andalusite surfaces, whereas those with higher molecular weights exhibited both physisorption and chemisorption during adsorption [28,29], and the interaction mechanism of andalusite, quartz, and dodecyl sulfonic acid was explored according to infrared spectroscopy, as shown in Figure 4 and Figure 5.

3.2.1. Infrared Spectroscopic Analysis of Interaction Between Andalusite and SDS

Analyzing the infrared spectrum of the andalusite single mineral in Figure 4 (spectrum 1), combined with the known structure of andalusite, the characteristic peak of asymmetric contraction vibration of silicon-oxygen tetrahedra was observed at 953.06 cm⁻¹, the characteristic peak of aluminum-oxygen octahedral vibration was observed at 525.61 cm⁻¹, and the characteristic peak formed by aluminum-oxygen hexahedral vibration was observed at 447.69 cm⁻¹.

Analyzing the infrared spectrum of SDS in Figure 4 (spectrum 2), it can be found that the elongated absorption peak of SDS methyl was observed at 2924.19 cm⁻¹ and 2851.94 cm⁻¹, the curved absorption peak of methylene group was observed at 1645.77 cm⁻¹ and 1469.18 cm⁻¹, and the vibrational absorption peak of sulfonic acid group was observed at 1174.49 cm⁻¹ and 1065.40 cm⁻¹ [29].

The analysis in Figure 4 (spectrum 3) shows that after the interaction between the surface of andalusite and SDS, the vibrational absorption peak of sulfonic acid group was observed at 1177.32 cm⁻¹ and 1062.73 cm⁻¹ on the curve, which indicates that SDS and andalusite surface have chemical adsorption, which corresponds to the previous research results [30].

Figure 4. Infrared spectroscopic analysis of the interaction between andalusite and SDS. (1) Andalusite, (2) SDS, and (3) andalusite + SDS.

Figure 4. Infrared spectroscopic analysis of the interaction between andalusite and SDS. (1) Andalusite, (2) SDS, and (3) andalusite + SDS.

3.2.2. Infrared Spectroscopic Analysis of Interaction Between Quartz and SDS

The infrared spectroscopy analysis of quartz is shown in Figure 5. The characteristic absorption band in Figure 5 (spectrum 1) is analyzed, combined with the known structure of quartz; the characteristic peaks of symmetrical contraction vibration of silicon-oxygen tetrahedron were observed at 781 cm⁻¹ and 461 cm⁻¹ [31], the bending vibration of aluminum-oxygen tetrahedron was observed at 689 cm⁻¹, and the characteristic peak formed by asymmetric contraction vibration of aluminum-oxygen tetrahedron was observed at 1093 cm⁻¹. The absorption peak at 3485 cm⁻¹ was the result of the hydroxyl contraction vibration formed on the quartz surface.

Figure 5 (spectrum 2) shows the infrared spectrum of SDS, when quartz interacts with SDS (spectrum 3); no obvious vibrational absorption peak of sulfonic acid group was found in the product spectrum, indicating that SDS has weak or insignificant adsorption on the surface of quartz single mineral [32,33]. The adsorption of SDS on quartz likely occurs primarily through electrostatic interactions with negatively charged surface sites (SiO⁻), constituting physical adsorption. Such interactions are less stable than the chemisorption formed between SDS and andalusite surfaces.

Figure 5. Infrared spectroscopic analysis of the interaction between quartz and SDS. (1) Quartz, (2) SDS, and (3) quartz + SDS.

Figure 5. Infrared spectroscopic analysis of the interaction between quartz and SDS. (1) Quartz, (2) SDS, and (3) quartz + SDS.

3.3. Quantum Chemistry of SDS Adsorption on Andalusite Surface

With the rapid development of density functional theory (DFT) and molecular dynamics methods, quantum chemistry research has been able to reveal the microscopic changes of the interaction between chemicals and mineral surfaces by investigating the crystal structure and adsorption of minerals at the molecular or atomic level [34,35,36,37,38], so the quantum chemical study of SDS adsorption on the surface of andalusite can be further analyzed.

3.3.1. Selection of Andalusite Surfaces

The dissociation of minerals tends towards the surface where the atoms act the weakest, i.e., the surface with the lowest energy. Andalusite crystals are composed of Si-O tetrahedra and Al-O octahedra, and the Si-O bond length and bond energy are shorter than those of Al-O in the andalusite crystal after structural optimization, so the Al-O bond is broken first during the crushing process. According to research, the main dissociation surfaces of andalusite are {1 1 0}, {1 0 0}, and {0 0 1} [39]. In order to determine the most stable dissociation surface of andalusite, the surface energy of three main dissociation surfaces was calculated, and the surface with low surface energy had a lower energy potential and was, therefore, the most frequently exposed cleavage surface.

The three-dimensional surface model of andalusite was established by Materials Studio software, and 1.5 layers were cut in the directions of {1 1 0}, {1 0 0}, and {0 0 1}, and a vacuum layer of 25 Å was added to the surface to avoid the influence of periodic structure. The 3D models of the andalusite {1 1 0}, {1 0 0}, and {0 0 1} surfaces are shown in Figure 6a–c.

In order to determine the most stable dissociation surface of andalusite, the surface energies of {1 1 0}, {1 0 0}, and {0 0 1} surfaces were calculated by using the dmol3 plate of Materials Studio 8.0 software, respectively. The formula for calculating the surface energy is as follows:

$${\mathrm{E}}_{\mathrm{s}\mathrm{u}\mathrm{r}\mathrm{f}\mathrm{a}\mathrm{c}\mathrm{e}}={\displaystyle \frac{1}{\mathrm{A}}}\left[{\mathrm{E}}_{\mathrm{s}\mathrm{l}\mathrm{a}\mathrm{b}}-\mathrm{n}{\mathrm{E}}_{\mathrm{b}\mathrm{u}\mathrm{l}\mathrm{k}}\right]$$

where E_surface refers to the surface energy of the crystal; A represents the total area in the surface model (including the upper and lower faces); E_slab represents the total energy of the surface model; E_bulk denotes the energy of a single atom or molecule in the bulk phase; n denotes the number of atoms or molecules in the surface model [39]. Under the same conditions, the surfaces of andalusite {1 1 0}, {1 0 0}, and {0 0 1} are shown in

Table 2. Surface energy of each surface of andalusite/(eV/Ų).

Andalusite surface	{1 1 0} surface	{1 0 0} surface	{0 0 1} surface
Surface energy	−3962.74	−4234.90	−4172.40

.

As can be seen from Table 2, the surface energy of the andalusite {1 1 0} surface is −3962.74 eV/Ų, the {1 0 0} surface is −4234.90 eV/Ų, and the {0 0 1} surface is −4172.40 eV/Ų. The magnitude of the surface energy can indicate the energy potential of the crystal surface, and the smaller the surface energy, the more stable the surface is. Among the main dissociation surfaces of andalusite, the surface energy of the {1 0 0} surface is the smallest, so the most important dissociation surface of andalusite is the {1 0 0} surface [38], so the calculation of the surface electronic structure and adsorption is mainly for the {1 0 0} surface of andalusite.

3.3.2. Adsorption of SDS on Andalusite {1 0 0} Surface

The molecular models of SDS were constructed and calculated by Materials Studio software, and the parameter settings were consistent with those calculated on the andalusite {1 0 0} surface. Structural optimization and energy calculations are performed on drug molecules. The molecular model of SDS is shown in Figure 7.

In order to reduce the influence of periodic structure on the adsorption of SDS on the andalusite {1 0 0} surface, a 2 × 2 × 1 andalusite surface model was established, and the SDS agent molecule was placed in the 2 × 2 × 1 andalusite surface model, so that the SDS molecule was perpendicular to the andalusite {1 0 0} surface, and the distance to the surface was within 3 Å, and the same parameter settings were used to optimize the structure. The adsorption configuration of SDS on the andalusite {1 0 0} surface is shown in Figure 8.

Table 3. Atomic displacement on the surface of andalusite {1 0 0} after adsorption of SDS.

Atomic Number	Atomic Displacement/nm
	ΔX	ΔY	ΔZ
1(Al)	−0.0019	0.0039	−0.0042
2(Al)	0.0042	−0.0018	−0.0059
3(Al)	−0.0043	−0.0071	−0.0063
4(O)	−0.0010	0.0011	−0.0008
5(O)	−0.0060	0.0011	−0.0023
6(O)	−0.0231	−0.0058	−0.0331
7(Al)	−0.0019	0.0013	−0.0023
8(Al)	0.0025	0.0031	0.0221
9(O)	0.0011	0.0011	−0.0042
10(O)	−0.0060	0.0019	0.0064
11(Si)	0.0004	−0.0029	0.0009
12(Si)	−0.0036	−0.0004	0.0026
13(Si)	0.0006	0.0006	−0.0022

lists the atomic displacements on the andalusite {1 0 0} surface following SDS adsorption, with negative signs indicating displacement opposite to the axial direction. The data reveal that atoms near SDS adsorption sites underwent significant relaxation. Specifically, aluminum atoms numbered 1, 2, and 3, along with an oxygen atom numbered 6, exhibited pronounced downward displacements. In contrast, silicon atoms showed negligible relaxation.

3.3.3. Mulliken Charge Analysis of Andalusite {1 0 0} Surface Adsorbed with SDS

Table 4. Mulliken charge layout of andalusite {1 0 0} before and after adsorption of SDS.

Atomic Number	1(Al)	2(Al)	3(Al)	4(O)	5(O)	6(O)	7(Al)
Net charge before adsorption (e)	0.688	0.688	0.688	−0.876	−0.936	−0.876	1.371
Net charge after adsorption (e)	0.65	1.024	0.769	−0.876	−0.956	−0.886	1.371
Atomic number	8(Al)	9(O)	10(O)	11(Si)	12(Si)	13(Si)
Net charge before adsorption (e)	1.371	−0.95	−0.95	1.915	1.857	1.857
Net charge after adsorption (e)	1.432	−0.949	−0.95	1.918	1.855	1.847

shows the mulliken charge of some atoms on the andalusite {1 0 0} plane before and after adsorption of SDS molecules. As can be seen from the table, the aluminum atom numbered 2 directly interacts with the single-bond oxygen atom of SDS, and the positive charge of the aluminum atom numbered 3 increases significantly after adsorption of the agent molecule, and the positive charge of the aluminum atom numbered 3 increases slightly. The oxygen and silicon atoms near the adsorption point have less variation in charge number.

3.3.4. Electronic Structure of Andalusite {1 0 0} Surface Adsorbed by SDS

The structurally optimized adsorption models were computed using the DMol3 module in Materials Studio 8.0 software. Electron density of states (DOS) analysis was performed on atoms proximal to adsorption sites to examine orbital variations in atoms interacting with reagent molecules.

It can be seen from Figure 9 that the density of states of aluminum atoms on the surface of SDS changes significantly before and after adsorption on the andalusite {1 0 0} surface, and the 2 s orbital and p orbital of aluminum atoms change slightly at −20 eV, but at the valence band, the density of states of the 2p orbital of aluminum atoms decreases significantly and shifts to the band. The density of states near the Fermi level decreased, indicating that the activity of aluminum atoms on the surface decreased after adsorption of SDS. On the whole, the density of states of aluminum atoms decreased compared with that before adsorption, indicating that the aluminum atoms on the andalusite {1 0 0} plane lost electrons during the adsorption process, and SDS underwent chemical adsorption on the surface of andalusite, which was consistent with previous studies [37].

As can be seen from Figure 10, the density of states of the 2 s orbital of oxygen atom at −20 eV basically did not change before and after the adsorption of SDS, and the density of states of the 2p orbital of oxygen atom at −15 eV~−10 eV moved to −10 eV~−5 eV, and the whole moved towards the Fermi level, indicating that the activity of oxygen atoms on the surface of andalusite was enhanced after the adsorption of SDS on the surface of andalusite.

As shown in Figure 11, the silicon atoms on the andalusite surface exhibited minimal variation before and after SDS adsorption. The density of states (DOS) of the silicon 2 s orbitals in the conduction band region showed reduced intensity, while the 2p orbitals within the energy range of −10 to −5 eV displayed a slight rightward shift (toward higher energy levels). Collectively, these changes remained relatively minor.

3.4. Effect of SDS on the Flotation Behavior of Andalusite and Quartz

Based on previous studies, this section explores the influence of SDS as a collector on the flotation behavior of andalusite and quartz. As an anionic surface activator, SDS itself has certain foaming properties and has good collecting performance for andalusite [40,41,42]. High-molecular alkyl sulfonates are widely used flotation reagents in the flotation practice of oxidized ores [43,44,45,46]. Sulfonic acid is a strong acid, and in a wide pH range, sulfonate is produced in ionic form in the flotation medium, and only in the strong acid (pH < 1~1.5) medium can sulfonate be hydrolyzed, which determines the characteristics of sulfonate that can achieve good capture results in a wide pH range [47].

3.4.1. The Influence of Medium pH Value on the Floatability of Minerals

By comparing the flotation test results of quartz and andalusite single minerals under different pH values in Figure 12, it can be seen that when SDS is used as a collector, andalusite has good floatability in a wide pH range, and the flotation effect is the best when pH is 3, and the recovery rate of andalusite is 85.39%. Quartz had poor floatability throughout the test conditions. The maximum recovery rate does not exceed 20%, indicating that SDS has a relatively weak collecting ability for quartz.

3.4.2. The Influence of Collector Types on the Floatability of Minerals

Furthermore, the influence of different collector types on the floatability of andalusite and quartz was investigated. Studies [41] indicate that fatty acids, alkyl sulfonates, and alkyl sulfates can all serve as collectors for andalusite. This section examines three representative collectors—sodium oleate, SDS, and sodium dodecyl sulfate. As shown in Figure 13, dodecyl sulfonic acid and sodium dodecyl sulfate demonstrate comparable flotation efficacy, with dodecyl sulfonic acid exhibiting slightly higher collecting power for andalusite. Sodium oleate shows distinct collecting performance for andalusite at pH 6.

3.4.3. Effect of SDS Dosage on Mineral Floatability

When the pH value of the medium was 3, the recovery rate of andalusite flotation was the highest, and the pH value of the stationary medium was 3, and the effect of SDS on the floatability of andalusite and quartz was explored (Figure 14). As can be seen from Figure 13, when the dosage of SDS in the system is less than 3.5 × 10⁻⁴ mol/L, the recovery rate of andalusite increases with the increase in SDS, and the highest recovery rate is 89.11%. The recovery rate of quartz increased slightly with the increase in SDS in the whole test range, and the change was not obvious; when the dosage of SDS was 4.0 × 10⁻⁴ mol/L, the recovery rate of quartz was 17.12%.

4. Conclusions

(1)

The zeta potential test indicates that the surface potential of andalusite decreases significantly under the SDS system. Under the test pH value of 3, the absolute value of the zeta potential on the surface of andalusite increases significantly, while the absolute value of the zeta potential on the quartz surface does not change significantly. This indicates that SDS has undergone strong adsorption on the surface of andalusite. However, the adsorption effect on quartz is not obvious. The FTIR analysis results further demonstrate that SDS undergoes chemisorption on the surface of andalusite, rather than physisorption.

(2)

Quantum chemical research was conducted on the adsorption of SDS on the surface of andalusite. It was found that the {1 0 0} surface of andalusite had the lowest surface energy and was the most important dissociation surface. After sodium dodecyl sulfate adsorbs on the {1 0 0} surface of andalusite, the surface atoms of andalusite show a slight downward relaxation. Mulliken charge analysis and density of states analysis indicate that the aluminum atoms on the surface of andalusite lose electrons and the positive charge they carry increases significantly, while the charge numbers of oxygen and silicon atoms change little. This indicates that sodium dodecyl sulfate adsorbs on the active sites of Al atoms on the surface of andalusite.

(3)

Flotation tests show that when SDS is used as the collector, andalusite has better floatability in a wide pH range, while quartz has poorer floatability. When the pH of the pulp was 3 and the dosage of SDS was 3.5 × 10⁻⁴ mol/L, the recovery rate of andalusite was 89.11% and that of quartz was 13.96%, indicating that andalusite and quartz had a good flotation separation effect under the SDS system.